Locomotives are used to haul freight and passengers over long distances. Locomotives have one or more sets of DC/AC traction motors that are powered by an electric generator turned by a diesel or a gas turbine engine. Recently, hybrid locomotives have started to gain acceptance where an energy storage unit is combined with the electric generator to power the motors when operating the locomotive in certain ranges, and for starting the prime mover of the generator.
One type of modern battery for the energy storage units of locomotives, or other energy storage needs, is a very high voltage multi-cell battery made by the Sodium Nickel Chloride (NaNiCl2) technology. These batteries have some characteristics which are helpful in monitoring their use and assist in their applications. Batteries of this type use as many as 480 battery cells coupled in series, where each cell produces 2.5 volts or less. The high voltage of such batteries is the result of a long serial chain of cells that adds the voltage of each cell to the others. Therefore, each battery contains many smaller individual batteries or cells, each with their own finite failure rate.
The individual cells, if they do fail, usually fail in a shorted condition with a resultant low impedance more than 99%+ of the time. The voltage output from this type of battery is relatively flat from 20% to 90% of its charged state. This allows a plurality of these batteries to be paralleled with others, even with some of their cells failed (shorted). The good cells of a battery having failed cells simply see fractional increases in voltage from the other paralleled batteries as their cell string has degraded operational performance with age. If two of the same type of battery are used in parallel, they should age at the same rate and thus balance each other. The limiting factor appears to be if the voltages between the parallel batteries become too markedly different, circulating currents will form between them.
Therefore, the inventors herein have recognized a need to monitor these batteries and to determine whether a predetermined number of cells have failed indicating a failed operational condition of the battery.
A battery can also have cells that fail in a cluster of cells. If the cells of this type of battery are not failing in random locations, it is likely there is physical problem within the battery and it may fail without further warning and should be removed from service.
Therefore, the inventors herein have recognized a need to monitor these batteries and to determine whether the cells have failed in a clustered or nonrandom order indicating a failed operational condition of the battery.